It starts with
Clean Air Vehicle Decal Issued Prior To January 1, 2017
By Vehicle Identification Number (VIN)
This list is current as of December 17, 2018 and subject to change.
These vehicles would be currently ineligible to re-apply for a new CA HOV sticker. So, if you're looking for used ones and you want to chance with it a CA car, you'll want to search for its VIN here. Not surprisingly, my current VIN and the VIN for my former leased '13 (for which I did get HOV stickers) are both in the list, as they should be.
And, if buying from out of state, besides Autocheck and Carfax to confirm it's never been registered in CA, you can double check this list.